import java.util.Scanner;
public class homewrok12 {
    public static void main(String[]args){
         Scanner scanner = new Scanner(System.in);

        System.out.print("请输入成绩：");
        int score =scanner.nextInt();

       if( score>=90||score<=100){
           System.out.println("A");
        }
         else if( score>=80||score<90){
            System.out.println("B");
        }
         else if( score>=60||score<80){
            System.out.println("C");
        }
        else if( score>=0||score<60){
            System.out.println("D");
        }

    }

}
